Two types of service or saddle clamps have been utilized for a number of years with main pipes when it is desired to install a branch connection and/or to tap into the pipe for connecting a future branch pipe. The first, and probably most commonly used, service clamp is the type which utilizes bolts or screws on opposite sides of the main pipe for clamping the assembly together to encompass the main pipe. While these clamps generally have one bolt or screw on each side of the clamps and are referred to as "two-bolt" clamps, they can have more than one bolt or screw if desired. This type of "two-bolt" service clamp has as its main advantage a uniform means of loading the sealing means carried by one of the saddle parts. In other words, the two saddle parts can have the screws or bolts tightened in such a manner that the saddle parts are clamped together along a line parallel to the axes of the bolts, thus applying the load uniformly to the sealing means. The main disadvantage or drawback of the two-bolt clamp is that it cannot be assembled quickly or easily about a main pipe, especially when it is necessary to utilize nuts with the bolts for drawing the two saddle parts together. Even in the situation where one of the saddle parts is provided with tapped apertures or holes for receiving bolts or screws, it will still require considerable manipulation of the parts to insert the bolts or screws into the tapped holes in the confines of a trench where the main pipe is located, especially when space for assembly is at a premium.
The second type of service clamp in considerable use today is a service clamp made up of two saddle parts and utilizing a single bolt but having a hinge between the two saddle parts so that the unit can be hinged into place and the single bolt or screw tightened. While this type of service clamp offers an advantage of easier assembly of the service clamp on the main pipe in limited space, it has a drawback in that the two saddle parts, when they are tightened about the main pipe, are pivoting on an axis parallel to the axis of the main pipe and, consequently, the sealing means carried by one of the saddle parts is unevenly loaded. There is a higher loading on the sealing means closer to the hinge axis than on the sealing means away from the hinge axis. This is especially critical when such service clamps are used on plastic main pipes since it not only puts a nonuniform load on the sealing means but, in effect, is also putting a nonuniform load on the plastic pipe which may, through cold flow, become out of round.